Carburizing steels containing chromium

ABSTRACT

A FAMILY OF STEELS HAVING BOTH HIGH HARDENABILITY AND HIGH IMPACT STRENGTH PROPERTIES THAT INCLUDE 0.18%-0.28% CARBON, 1.01%-1.17% MANGANESE, 0.15%-0.17% MOLYB-%-0.28% DENUM, 0.48%-0.60% CHROMIUM, AND TRACE AMOUNTS OF NICKEL.

June 13,1972 w. P. YOUNG ETAL 3,669,652

CARBURIZING STEELS CONTAINING CHROMIUM Filed April 20, 1970 w BAR-- BAR- A o z 4 6 8 1o 12 74.16 78 20 222426 DISIZM CE FROM OUENCl/ED END OFJOM/IW EAR IIV 5/X7FEA 77/5 OF AN l/VCH I Z ggfdm 3,669,652 Patented June 13, 1972 3,669,652 CARBURIZING STEELS CONTAINING CHROMIUM William P. Young, La Grange, and John A. Halgren,

Downers Grove, Ill., assignors to International Harvester Company, Chicago, Ill.

Filed Ap 20, 1970, Ser. No. 29,884 Int. Cl. C22c 39/14 US. Cl. 75-126 C 1 Claim ABSTRACT OF THE DISCLOSURE A family of steels having both high hardenability and high impact strength properties that include 0.18%-0.2-8% carbon, 1.01%-l.l7% manganese, 0.15%-0.17% molybdenum, 0.48%-0.60% chromium, and trace amounts of nickel.

BACKGROUND OF THE INVENTION This invention relates to carburizing steels and more particularly to a family of carburizing steels especially suited for applications that require high impact strength.

Carburizing steels are used in applications where high surface hardness and high toughness or impact strength in the core are desired. Articles such as gears, splined shafts, and the like are typical examples of products which utilize carburizing steels. In a gear, for example, the gear teeth must possess extreme hardness to withstand the abrasion forces they encounter. But also the internal portion or core of the gear must posses high impact strength to absorb violent shocks.

In the past it has been difficult to obtain the requisite hardenability in carburizing steels and still retain a high degree of impact strength. However, it was found that by adding substantial amounts of nickel to a steel the requisite degree of toughness or impact strength could be maintained. For example, the AISI-SAE 8620H-8 627H family of steels was developed containing 0.35% to 0.75% nickel, in combination with other alloying elements such as manganese, chromium and molybdenum. These steels have served quite satisfactorily in carburizing type applications. However, the economic realities are that nickel is becoming increasingly shorter in supply and concurrently increasingly higher in cost. Accordingly, it would be most beneficial to develop a nickel-free carburizing steel that duplicated or excelled the hardenability and impact strength charcten'stics of the 8620H-8627B family of carburizing steels.

SUMMARY OF THE INVENTION This invention responds to the need for a nickel-free carburizing steel and it most unexpectedly has been found that not only hardenability but also the impact strength characteristics of the 8600H carburizing steels can be duplicated in a steel that is free from nickel. The family of steels which forms the subject of this invention has a carbon content of about 0.18 %0.28%, a manganese content of about 1.01%1.17%, a silicon content of about 0.20%-0.35%, trace amounts of nickel, a chromium content of about 0.48%0.60% and a molybdenum content of about 0.15 %0.17%, a maximum phosphorous content of about .035 and a maximum sulfur content of about .04%.

BRIEF DESCRIPTION OF THE DRAWING The features and characteristics of this invention will become more apparent in the following description when read in conjunction with the figure which is a graphical interpretation of the measured hardenabilities of steels produced in accordance with this invention and the 8620H- 8627H carburizing steels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The features of this invention are best understood by way of examples that illustrate the unexpected results obtained by this invention. The following Table I sets forth the preferred compositional ranges of the alloying elements in this invention.

TABLE I Preferred composition Element: Weight percent Carbon 0.18-0.28 Manganese 1.01-1.17 Silicon 0.20-0.35 Chromium 0.48-0.60 Molybdenum 0.15-0.17 Phosphorous, max. 0.035 Sulfur, max. 0.04 Nickel Trace Iron Balance It will be understood that some residual nickel will be present in most steels because of current manufacturing processes. characteristically the residual nickel content will be between 0.00% and 0.04%. As used herein the term trace when referring to the nickel content means 0.04% maximum. Furthermore it should be understood that residual amounts of elements that are not listed in Table I may also be present.

The family of steels forming this invention vary the carbon content and hold the other alloying elements within the ranges set forth in Table I. Ideally, the alloying elements that form the most critical components of the steels would constitute about the following weight percentages: 1.09% Mn, 0.54% Cr, and 0.16% Mo.

Hardenability examples Two test specimens falling within the preferred range of compositions shown in Table I were prepared for a standard Jominy Hardenability Test. The test bars were prepared in the usual manner and their compositions in weight percentages are set forth in Table II.

TABLE II Hardenability specimen compositions Percent Elements Bar A Bar B Carbon 0. 26 0. 26

Bal. Bal.

TABLE III Measured hardenability data Max., Min., Bar A, Bar B, R6 6 6 R6 Impact strength examples Standard .394" square Charpy V-notched bars were austenitized, quenched and tempered to a hardness of 28 R Nine test bars were made of steel utilizing the principles of this invention having the compositional range tabulated in Table IV. Ten test bars of 8620H steel were made for comparison purposes.

TABLE IV Composition of Charpy test bars The bars were tested at 0 F. and -40 F. and produced the results shown in Table V.

TABLE V Impact energy absorbed to fracture, ft. lbs.

Test temp., F. 862011 Bars 1-9 Average 105 113 Average 101 100 From Table V it may be seen that the low temperature impact strength of the steel utilizing the principles of this invention was substantially identical to the 8620H material and at 0 F. was somewhat higher in impact strength.

Nil ductility transition temperature tests were performed using ASTM E 2-0866T procedures with a modified lP-3 specimen, i.e. .625" x 1.750" X 5.00". Eight test bars were produced utilizing the principles of this invention and having the composition set forth in Table Vil. For C0111.

parison purposes test bars were formed of 8622H steel.

TABLE VI Composition of nil ductility test bars Element: Weight percent Carbon 0.26 Manganese 1.15 Silicon 0.22 Chromium 0.52 Molybdenum 0.15 Phosphorous 0.02 Sulfur 0.02 Nickel 0.00 Aluminum 0.06 Iron Balance The measured nil ductility transition temperature for bars 1-6 was --'50 F. (46 C.). That compared to a measured nil ductility transition temperature of 60 F. (5 1 C.) for the 8622H material. Thus, in both Charpy impact strength tests and nil ductility transition temperature tests the steel produced in accordance'with the principles of this invention was found to be out of substantially identical impact strength and toughness characteristics as the 8620H-,8627 materials.

Thus, a new composition for carburizing steels has been developed. It has the qualities of high hardenability, high impact strength and absence of nickel.

We claim:

1. A carburizing alloy steel having high hardenability and high impact strength characteristics that consists in weight percentages of:

0.180.28% carbon, 1.01-1,17% manganese, 0.20-

0.35% silicon, 0.48-0.60% chromium, 0.15-0.17% molybdenum, 0.035 maximum phosphorous, 0.04% maximum sulfur, 0.04% maximum nickel, and the balance iron.

References Cited UNITED STATES PATENTS 3,463,677 8/ 1969 Nakamura 126 C 2,276,376 3/1942 Deubel 75-126 R 3,328,211 6/1967 Nakamura 75--126 C 3,554,734- 1/1971 Kikkawa 75-126 R HYLAND BIZOT, Primary Examiner 

